A touchpad is a pointing device that may be used, like a computer mouse, to provide an interface to an electronic device. A touchpad is a specialized control surface that converts the motion and/or position of a user's fingers to a relative position on a screen of the electronic device. A touchpad is a common feature of laptop computers and also used as a substitute for a computer mouse where desk space is scarce. Touchpads can also be found on a variety of portable electronic devices such as personal digital assistants (PDAs), portable media players and mobile telephones.
Typically, touchpads used conductive or capacitive sensing to detect the motion or position of a user's finger. A matrix of sensing elements is required.
An example touchpad is disclosed in U.S. Pat. No. 5,305,017. In this approach, a series of conductors are arranged in an array of parallel lines in two layers, separated by an insulator and crossing each other at right angles to form a grid. A high frequency signal is applied sequentially between pairs in this two-dimensional grid array. The current that passes between the nodes is proportional to the capacitance. When a virtual ground, such as a finger, is placed over one of the intersections of the conductive layer, some of the electrical field is shunted to this ground point, resulting in a change in the apparent capacitance at that location that is sensed.
Micro Electro Mechanical Systems (MEMS's) exploit the mechanical properties of silicon and the techniques of micro-machining to provided integrated mechanical structures sensitive to vibration, displacement, acceleration and rotation. MEMS technology has yielded a new generation of compact, cost effective and sensitive sensors. While conventional microelectronics development focuses on incremental improvements of a well-established technology, MEMS-based sensors challenge the way designers work, compelling them to think three dimensionally and to acquire a unique blend of multi-disciplinary skills combining electrical, semiconductor, and mechanical design.
The new generation of sensors, based on MEMS technology, can be classified belong four families: motion sensors, pressure sensors, RF devices and micro-fluidic devices.
MEMS-based motion sensors, such as linear accelerometers and gyroscopes, are devices that are able to sense linear acceleration or rotation rate.
A variety of MEMS-based sensors, including linear accelerometer sensors, are available commercially from companies such as STMicroelectronics.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.